Multiplex communication system



Nov. 1, 1932. w. ILBERG MULTIPLEX COMMUNICATION SYSTEM Filed Jan. #[1931 m w w y 1 w H H M u m c k M m R m w w m W N 1 R k n u m m 5 MW #4 ATTORNEY Patented Nov. 1, 1932 UNITED, STATES PATENT OFFICE WALIDEMAR ILBERG, OF BERLIN, GERMANY, ASSIGNOR- 1'0 TELEFUNKEN' GESELL- SCHAFT FUR DRAHTLOSE TELEGBAPHIE M. B. 31., OF BEItLIN, GERMANY A CORIO- RATION or GERMANY MULTIPLE! COMMUNICATION SYSTEM Application filed January 7, 1931, Serial No. 507,065, and in .Germany January 8, 1930.

The present invention relates to a method of and means for radio multiplex telegraphy.

Radio communication channels comprising transmitter, and receiver as a general rule permit only of the simultaneous transmission of one message. To be sure, it is known the prior art that, for the purpose of obtaining with a given radio equipment several simultaneous communication channels, recourse may be had to the scheme to modulate the radio frequency carrier wave with a correspondingly great number of tonal or superaudible frequencies, and to render these in turn to act as carriers for signal modulation., In such cases, the various ensuing communication channels are separated at the receiving end, for instance, by the aid of suitable filter circuits. However, such a scheme involves the disadvantage that in such division into n many channels, each of the chan-- nels will share only of the aggregate transmitter energy, and the resultant efiiciency of the equipment is only low.

The principal object of the present invention is, therefore, a multiplex and especially a duplex telegraphy method which is free from the above mentioned disadvantage. The underlying idea shall be described in what follows by means of two simultaneously operated channels, it being evident to the man trained in the art that the application of the basic principle of this invention to three or more channels is readily feasible; and each one of such channels is readily operable for code or picture telegraphy.

In all telegraph systems employed for radio communication work, the constituent signals involve fundamentally two operating conditions of the key, viz., dash and spacel, resulting in signal and space currents. The same condition holds good for picture telegraphy provided half-tone transmission is dispensed with, or if the latter is reduced to black-white contrast transmission by means of the method based upon varying lengthoof dots. Hence, when slmultaneously operating it 'many channels, there result 2 many keylng combmations, 1n other words, fourcomblnations 1n the case of two channels, 1. e.,

(1) transmitter 1 space (2) transmitter 1 dash (3) transmitter 1 ace transmitter'2 dash (4) transmitter 1 ash transmitter 2 dash.

In order to characterize the said possible key operating conditions, certain frequencles transmitter 2 space transmitter 2 space radiated oil from the transmitter are to be used; and these frequencies, as in radio telephony, are to be radiated off in the form of modulating frequencies of a carrier wave. However, the extent of shifting the carrier lzing the key operating conditions. This latter method, fundamentally speaking, is identical with the method first referred to as soon as a side band including the carrier wave is suppressed at the sending end.

In case of transmitter modulation with tonal frequencies defined by the keying combinations that are used, it would be jof advantage to omit the one which characterizes simultaneous spaces or-intermissions for all channels, and to replace the same by the absence of modulation or insuflicient radiation of the transmitter.

A transmitter scheme working according to this principle is illustrated in Fig. 1 of the accompanying drawing, and a-suitable form of construction of a receiver equipment adapted to effect separation or filtering of the two communication channels is illustrated by Fig; 2, where Fig. 2a indicates conventionally a receiver, and Figs. '26 and 20 indicate the range of the filters cooperating with the receiver.

By the following description, when making reference to the drawing, the two communication. channels which are to be used simulwave itself could be employed for characterand the coordination of the modulation frequencies shall be given by the following scheme:

Channel I Channel 11 Modulation Space Space None Space Dash w; Dash Dash ")2 Dash Space w:

Waves or frequencies e0 w and w are produced by the three generators1 ,2 and 3. respectively, which may be any well known type of thermionic tube generators, for example, and these generated frequencies are fed to the modulating means 4 of the'radio frequency transmitter 5 by way of relays 1a, 2a and 3a coordinated thereto. The control of the relays 1a, plished through the use of'keys or keying relays T and T5 corresponding to the channels in a manner that will be evident from the above description. Instead of keys T and T and in lieu of relays 1a, 2a, 3a, recourse could conceivably be had also to inertialess controlling means such as thermionic tubes, and these in turn could be controlled by scanning actions, such as with photoelectric cells in picture telegraphy where an image of some object is to be received.

Now, referring to the receiver, the audio frequency waves obtained by demodulation from the incoming radio frequency band are brought to act upon two selectively actingmeans such as filters 1 and-2 which are coordinated to the two communication channels. Suitable transmission ranges of these two filters are shown in diagrammatic man ner by Figs. 2b and 20. Connected to the output of the filters is the indicator means for the two channels. The indicators may be telephone receivers, undulators, picture recorders, and the like.

It will be clear that during the absence of any audio frequencies, that is, an unmodulated condition of transmitter, none of the said indicator means will be operated, whereas when wave at), comes in only channel I is ener ized; in the case of wave w both channel and channel II are operative and when wave 'w is received only channel II is excited, in accordance with the corresponding positions of the transmitter keysT and T of Fig. 1. It will, ofcourse, he understood from the above description that the necessary selector means could be connected in the receiver equipment also at some other place, for instance, in an intermediatefrequency amplifier stage instead of in the manner above'described, Y

In lieu of three separate tonal generators or oscillators shown by Fig. 1, 'a single oscillator might be provided in the transmitter equipment, and the frequency or wavethermionic generator,

2a, and 3a is accomfrequency o;

length of said oscillator might then be altered in accordance with the key positions. This end could be attained, among other ways, by inserting or cutting out capacity (condensers) in the oscillation circuit of the or else by variation of direct current magnetization of an ironcored inductance coil. This latter methodis particularly suited for high-speed key operation in which mechanical parts such as relay keepers are to be dispensed with, as, for example, in scanning in picture telegraphy. In this case, it will generally be found to be impossible or at least rather diflicult to characterize and define simultaneous spacing 0 all channels by the absence of the modulation frequency; on the contrary, it would be of greater advantage to radiate a modulator The latter could be eliminated at the receiving end by providing a stopper circuit for this particular wave-length, or else by shifting the whole incoming audio frequency band in the sense of lower frequencies by an amount equal to 40 by the provision of a heterodyne.

To diminish the disturbing action of selective fading, it may prove to be of advantage to utilize waves for modulat'ng the transmitter which are altered or wobbled in rapid succession about a median value inside a relatively narrow range rather than fixed wave-lengths. Other modifications will also sug est themselves, and the invention is, there ore, to be interpreted in its broad sense as defined by the hereinafter appended claims. v

Having now described my invention, what I claim and desire to secure by. Letters Patent is the following:

1. A multiplex telegraphy system comprising a keying means for. each channel in the multiplex system,

means having a marking and spacing posltion, an energy transmitter, and means coordinated with said keying means for separately modulating said energy transmitter by a plurality of modulation frequencies corresponding in number to the possible combinations of simultaneous operating condi' 'tions of the keying means for the several channels.

2. A multiplex telegraphy system comprising a keying means for each channel in the multiplex system, each having a marking and spacing position, a plurality of sources of different modulation frequencies corresponding in number to the possible combinations of simultaneous operating conditions of the keying means for the several channels, an energy transmitter, and

means connected with said keying means for of said keying means position of said keying 3. A multiplex telegraphy system comprising a keying means for each channel in the multiplex system, each of said keying means having a marking and spacing position, an energy transmitter, means coordinated with said keying means for separately modulating said energy transmitter by a. plurality of modulation frequencies corresponding in number to the possible combinations of simultaneous operating conditions of the keying means for the several channels, means for receiving the energy transmitted, means for restoring the several transmitted modulation frequencies at the receiver, and a plurality of signal indicating means coordinated to the various channels for indicating the keying positions of the several keys of the transmitter.

4. A multiplex telegraphy system compris-' ing a keying means for each channel in the multiplex system, each of said keying means having a marking and spacing position, an

. energy transmitter, a plurality of sources of tion frequencies tion,- a

modulating currents, each of a different frequency and corresponding in number to the possible combinations of simultaneous operating conditions of the keying means for the several channels, means coordinated Withsaid keying means for modulating said energy transmitter by a single one of a plurality of sources of modulation frequencies for each separate position of said keying means, means or receiving the energy transmitted, means for restoring the several transmitted modulaat the receiver, and a plurality of signal indicating means coordinated to the various channels for indicating the keying positions of the several keys of the transmitter.

5. In a two channel multiplex communication system, a pair of keying means for producing separate signal indications, each of said keying means having a marking and spacing position, a transmitter, a plurality of oscillation generators for generating frequencies of predetermined value, means for modulating said transmitter by a separate one of said generated frequencies for marking positions of both of said keying means or for spacing on one of said keying means and marking on the other, andmeans for interrupting the transmission for spacing on each of said keying means. I

6. In a multiplex system, a receiving means for transmitted signals, a pair of filters connected with the outplt of said receiving means, each of said filters having overlapping cut-ofi' points, a signal indicator connected with each 'of said filters, and means provided by said overlapping cut-ofi points on said filters to cause said indicators to operate separately or collectively in accordance with received signal impulses for simultaneously indicating a plurality of'received messages. 7. In a system for multiplex communicatransmitter, a plurality of keys for modulated by determining messages sent out from the transmitter, a plurality of oscillation generators each of different frequency for modulating said transmitter, and means cooperating with the keys for modulating said. transmitter by a single one of said different frequencies for different possible combinations of spacing 122nd marking positions of said plurality of eys.

8. In a duplex communication system for the transmission of code messages, a transmitter, a. pair of keys for transmitting space and mark typeof messages, means for separately modulatingvthe transmitter at a plurality of different frequencies corresponding in number to the possible combinations of space and mark, key positions of the pair. of keying means, and means controlled by the position of said keying means for controlling the modulation frequency of said transmitter.

9. A method of multiplex communication comprising producing a plurality of messages each as a series of spacing and marking impulses, generating a plurality of modulation frequencies in excess of the number of mes sages simultaneously transmitted, limiting the effective modulation frequency to a single frequency at any instant in accordance with the combinations of spacing and marking positions of the various messages simultaneously transmitted, and transmitting a signal a separate one of the several modulation frequencies for each of the possible combinations of spacings and markings of each of the messages transmitted.

10. The method of determining and separating a plurality of simultaneously transmitted messages which comprises receiving j signals modulated at a plurality of different frequencies for the possible combinations of spacings and markings on each of the simultaneously transmitted messages, filtering the received signals to separate the several modulating frequencies, causing predetermined modulation frequencies to overlap in the filtering for predetermined conditions of marking and spacing on each of the channels, and producing indications of the spacing and marking positions on each of the message channelsin accordance with the filtered received signals.

11. A multiplex signalling system comprising signal producing means, a plurality of 0scillation generators each of different frequency, a transmitter, and means operative to connect a different one of said oscillation generators with said transmitter to modulate the transmitter at one of said generated frequencies for each combination of the presence or absence of signals on said signal producing means.

12. A multiplex signalling system comprlsing a pair of keying instrumentalities each having on and off positions for indicating the presence or absence of energizing impulses thereon, a signal transmitter, a plurality of oscillation generators each of difierent frequency, means to connect a single one of each of said oscillation generators with said transmitter so as to modulate the transmitter at one of said frequencies for each combination of on and off position of each of said keying instrumentalities, which combination includes an on position of at least one of said keying instrumentalities to change the modulation frequency on said transmitter, and means pcrative from the on position of each of saidplurality of keying instrumentalities for in- 'cators,

ad acent modulation frequencies connected terrupting signals on each of said keying instrumentalities.

13. A receiving system for transmitted signals modulated at each of aplurality of modulation frequencies, comprising a signal receiving amplifier, a plurality of signal indiand a filter circuit tuned to pass two with each of said signal indicators so that by the overlapping cut-oil points of said filters said si al indicators operate individually or collectively to indicate simultaneously a-plurality of reoeivec%V messages.

ALDEMAR ILBERG.

the said modulation frequency on said transmitter during periods of absence of 

